Diamonds have an allure unlike any other gemstone. Through the ages, they have been sought after for their characteristically brilliant qualities and have been the subject of great treasures. There is such high demand for the stones, even today, that considerable research is under way to produce synthetic gems.
Gemstones such as cubic zirconium and silicon carbide, also known as moissanite, have become increasingly popular because they are almost indistinguishable from real diamonds with the naked eye. As a result, the market is flooded with these synthetic look-alike gemstones. Unfortunately, some of these gemstones, significantly lower in value, are sold as natural diamonds to the dismay of many unknowing purchasers. To combat these fraudulent or mistaken sales, several techniques have been suggested to determine the authenticity of a diamond.
One technique involves a relatively complex x-ray test that takes several hours to perform. Unfortunately, the associated testing apparatus is costly and most jewelers are not equipped with the instrumentation required to perform the test. Another technique involves testing the hardness of the gemstone by scratching or otherwise marring the surface of the gem. Needless to say, this method of defacing a gem is highly undesirable because it negatively impacts the value of the gem and alternative nondestructive methods of testing are available today.
Alternative non-destructive test methods include testing the optical transmissivity and thermal characteristics of a gem to determine whether it is a real diamond. In particular, one optical method involves transmitting light waves through the gem under test and, thereafter, determining which wavelengths of the light source have been absorbed. Generally, diamonds reflect certain wavelengths of light while silicon carbide absorbs certain wavelengths of light. Unfortunately, determining the authenticity of a diamond based on this method is not failsafe because the transmissivity of some diamonds is effected by their cut and mass.
Another non-destructive method of determining the authenticity of a diamond involves testing the thermal conductivity of the gem. The test process includes heating a probe of known mass to a predetermined level and touching the probe to the gem under test. A thermistor in the probe is used to detect the dynamic change in probe temperature as the gem absorbs heat energy from the probe thereby reducing its temperature; i.e. the temperature of the probe gradually decreases depending on the rate at which heat is absorbed by the gem under test. Based on the rate of temperature change of the probe, the thermal conductivity of the diamond is determined and, thus, whether the gem under test is a real diamond. The thermal conductivity test is widely used to distinguish cubic zirconia and diamond, but silicon carbide has a thermal conductivity which is about equal to that of diamond, making the test impractical for those gemstones.
Electrical resistance measurements have been used to distinguish gems. In particular, some thermal testers have included a two electrode device for detecting when a thermal test probe is erroneously in contact with a metal, which has a thermal conductivity very similar to that of natural diamonds. This prevented an operator from falsely identifying a gemstone as diamond when, in fact, the measuring device was measuring the thermal conductivity of the metal instead of the gem. Occasionally, this low impedance detection circuit, when used correctly, could positively indicate that a gem under test was a member of a more conductive class of moissanite. The tester, however, was unsuccessful at identifying the balance of moissanite gems that were less conductive.
Since the value of a diamond is in part dependent upon its weight, it is not uncommon to increase its size and, therefore, apparent value, by depositing simulant diamond material on an uncut or partly cut natural diamond. This combination, namely real and imitation diamond, is particularly difficult to distinguish from a completely natural diamond because in some respects the imitation-natural stone has qualities of a natural diamond while in other respects the imitation-natural stone has the qualities of a synthetic stone.